Any amount charged to the owner of land in accordance with the provisions of RCW 15.09.080 and 15.09.090 shall be paid by such owner within sixty days of the date in which he or she was billed for such amount. If payment is not made within such sixty day period, the amount of such charge, together with a ten percent penalty surcharge, shall, for purposes of collection, become a tax lien under RCW 84.60.010, as now or hereafter amended, and shall be promptly collected as such by the county treasurer: PROVIDED, That where good cause is shown the board may extend for an additional two months the time period during which payment shall be made.